The following three projects have benefited from experiments performed at the Cornell High Energy Synchrotron Source. -Lambda phage lysozyme lysozyme from lambda phage, like other lysozymes, is capable of hydrolyzing bacterial cell-walls. However, the mechanism by which this hydrolysis is accomplished differs dramatically from that of other lysozymes (e.g. T4 - and hen egg-white lysozyme). We have recently solved the structure of the enzyme in the presence of an inhibitor to 2.7 Angstrom, by molecular replacement. The structure provides insight into the unique mechanism employed by this enzyme for hydrolyzing the peptidoglycan layer of bacterial cell-walls. - fungal homoserine dehydrogenase Homoserine dehydrogenase from fungal sources has been shown to be an excellent target for antifungal agents. Since this 370 residue enzyme lacksany methionines, we have pursued the multiple isomorphous replacement method for determining the three-dimensional structure. Optimized anomalous derivative data collected at the CHESS F2 beam-line has resulted in a partial tracing of the structure. Unfortunately, severe non-isomorphism between crystals has hampered rapid progress. - AAC(6')-Ii AAC(6')-Ii is a bacterial enzyme responsible for bacterial resistance against aminoglycoside antibiotics. Two MAD datasets of a selinomethionine derivative of this enzyme were collected at the CHESS F2 beam-line. We have successfully solved the structure, and are currently refining the atomic model. The significance of this structure determination considering the problem of antibiotic resistance is obvious.